RELATIONS TO EXTINCT ORGANISMS. 8i 



parously, and that we might to this fact ascribe the second 

 pecuharity of the genus — namely, the existence in many of the 

 coralhtes of imperfect vertical partitions (generally one or two 

 in number in any particular tube). These partitions appear 

 in tangential sections of the corallum as blunt tooth-like pro- 

 cesses projecting into the interior of the corallites (fig. lo, a), 

 and they might be taken at first sight as being " septa." They 

 are, however, wanting in many of the tubes ; and there is little 

 doubt that they are really due to the fact that the corallites 

 which possess them have begun to divide by fission. 



While the points above noted enable us to separate the 

 species of Chcstetes, Fischer, from those of Montintlipora, it 

 is not so easy to definitely separate the latter from Stcno- 

 pora, Lonsd. The typical species of Stcnopora, Lonsd. {iion 

 M'Coy) possess a ramose or sublobate corallum, composed of 

 tubular corallites, which are nearly vertical in the centre of 

 the branches, and radiate outwards from an imaginary axis 

 to open on all points of the free surface. In the centre of 

 the branches the corallites (like those of the dendroid species 

 of Montictdipord) are thin-walled and polygonal, but they be- 

 come thickened as they approach the surface, and they are never 

 amalgamated with one another by their walls. The thickening 



1 



m 



m 



Fig. II. — A, Poi-tiou of a branch of S/LiioJ^ora Jackii, Nich. and Etli. jun., split open, of the 

 natural size ; B, Portion of tlie same enharged, showing the annulations of the tubes in 

 their outer portions ; c, A few of the tubes of the same still further enlarged, showing 

 the mural pores. Permo-Carboniferous formation, (Queensland. 



of the walls of the tubes in the latter portion of their course 

 takes place in the same way as in many JMontic^iliporcc {e.g., 

 M. tiunida, Phill.) — namely, by the deposition of superimposed 

 lamelLne of sclerenchyma round the growing margins of the 



